Automatic diffuser control for air-breathing engines



AWM/7M.

inw/x Jan. 27, 1959 AUTOMATIC DIFFUSER CONTROL FOR AIR-BREATHING ENGINES fl M i. J m E f llllllllllll llllllll Il W y .m QM M 7.. w T. fa. ,M U l a 5. ,a /V W n 4@ 1 a 4 Z ff H 5 5 0 i. mm, 5 j MM 1 |11, .i 1|1||i|1 INN f/m w/. n.. Mw... w Wg w .M fn ,.W Za y u M L V||| QA .MQQKN a United States Patent() "ice l AUTOMATIC DIFFUSER CONTROL FOR AIR-BREATHING ENGINES Anthony Demetriades, Pasadena, Calif., assignor to Lear, Incorporated, Santa Monica, Calif.

Application March 14, 195s, serial No. 493,939 4 Claims. (ci. eti- 35m This invention relates to air-breathing engines of the type used in aircraft flown as supersonic speeds, and more particularly to automatic control of inlet air for such an engine to effect its operation at maximum efficiency at any Mach number of flight.

It is well known that in an air-breathing power-plant vvfor an aircraft flown at some given supersonic speed, the

air pressure recovery needed for optimum thrust is obtained by means of a diifuser hxed at the entrance of theV engine. With an arrangement known as the spike diffuser, inlet air flows between the surface of a conical center-body and the inner surface of the Cowling of the means for Vautomatically controlling the inlet air to an 4'air-breathing engine for .aircraft so that suchl engines l,will `operate 'at maximum efficiency at any supersonic "speed Mach 'number of flight.

A It is vanother object of this invention to provide, foran air'jbreathing engine of a supersonic aircraft,l an automatically variable diffuser to effect maximum pressure lrecovery and hence maximum efliciency of lthe engine atany speed of flight of the aircraft.

`It is still another object of thisV fnventiori to provide, for an air-breathing engine, V'a variable diffuser and an 'automatic control system to 4manipulate the diffuser and to `control the inlet air so the engine will operate at 'maximum enciency at substantially all supersonic speeds. The 'above and other objects and advantages ,of this l'invention will become apparent from the following de- 'Scripti'on taken in conjunction with the accompanying The scope of the invention is pointed out in the appended claims. In the drawing,

Y Fig. l is a perspective view of 'the `inlet end of an 'airfuser, in accordance with 'this invention;

Fig. '2 is a blo-ck diagram to illustrate a suitable control ysysterii for automatic diffuser control, further in accordanc'e with this invention;

Fig. 5 isa series of curves to illustrate etliciency of Briey, this invention comprises Vthe measurement of ftheactual ilight Mach number aindithe Mach number 'Iloff air ilow behind a diffuser-spike within the lCowling :j of the engine.

Signals'are derived which Yrepresei'it the "p'sent' position of the spike and the two Mach numbers,

,bravi/ing, in which a preferred arrangement is illustrated by way 'of example.

f'breathing aircraft engine provided with a .variable 'diff Y'operation of an aircraft engine having a diffuser which fis automatically positioned by the system of Fig. 2.

A2,810,601 Patented Jan. 27, 1959 'andy this signal information is correlated to developa ycontrol; signal whihrepresents the optimum position for the spike. Finally, the spike is moved to a position in response to vthel control signal. Y n

Referring'to Fig. 1, an aircraft of the air-breathing ty`pe i'sillistit'edv with a conoidal diffuser element or spi-ke 10 located within the mouth of, the cowling 12 of an engine. Spike 10 is adapted for axial movement within the mouth of lthe Cowling 12, as indicated at 14. For the purpose of this invention,v spike 10 is movable to permit it tofbe Iklocated at the best: position for any given speed of flight which will admit air flow to the engine for maximum operating eiiiciency;

A suitable system to control the position of diffuser Spike 10 is illustrated in Fig. 2 Referring to Fig. '2, a Mach member transducer 16 is adapted to supply signals to al computer 18. A position pickoff or sensing device 159 is adapted to effect a signal input to the computer which v'represents 4the position of the spike 10 within the Cowling 1-2. The computer 18 is coupled to Aa differential amplifier 20, along with the output of a Machnumber transducer 22. 'Signals from the differential amplifier 20 are applied to a relay network 24, and a diffuser actuator 26 mechanically -coupled to spike 10 is adapted a 'sents the Mach number of the air flow at point F. The

differential amplifier 20 therefore effectively responds-"t0 an error signal representing the Adifference between the signals from computer 18 and transducer'ZZ to apply a command 'or control signal to the relay network 24.

Relay network 24 lmay be a conventional polaritysensitive switching circuit adapted to translate signals to its output which correspond to the polarity of the input signals. Actuator 26 is a suitable electro-mechanical device to move spike `10 in a direction depending upon the polarity of the 4signals from the relay network. :lf the position of yspike 11l) is the proper one for the particular speed of flight, the comparison of the outputs of computer 18 and transducer 22 results in a zero loutput from differential amplifier 20 and relay network 24.

Mach-number transducersl 16 and 22 are conventional and may, for example, be of the type illustrated and described in the publication, Kollsman Aircraft Instruments v(published yby Kollsman Instrument Corporation, 1954). Computer 18 may comprise conventional function generators adapted to -develop a signal output which vbears ya 'desired functional relation to two input signals, examples of which may be found in the publication, Electronic Analog Computers by G. A. Korn and T.

vTM. Korn (McGraw-Hill Book Co., New York, N. Y

Theposition pickoi device 19inay be la potentiometer device having its sliding arm mechanically coupled to spike 10 and movable with the diffuser to cause a signal representative of its position to be applied to computer 18.

AIf the actual flight Mach number is designated M1, 'and Athe signal due to positioning of pickoff 19 Tis d'e'sigf 'nated'a s"x, computer 18 develops a signal f(x, M1) which jireprsents the' optimum VMach number (MFL), for air .How behind the diffuser. This 'may be expressed Ias YWhere MF represents the 3 Mach number at location F. Transducer 22 applies a signal to differential amplifier 20 which represents MF. The output of amplifier 20 is a signal whichhas a magnitude representing the AdifferenceV between the magnitudes of the` inputv signals thereto and a polarity corresponding Yto the polarity of the greater of the two signals; Accordingly, relay network 24 will'eifect operation of actuator 26 to move spike in the proper direction and through the proper dis v tance, as previously explained. If the signals from coinputer 18 and transducer 22 are identical in magnitude `and of opposite polarity, the command signal will, ofv

course, be zero. f 'Y Y Y Y To further aid in understanding this invention, refer- Yence will be made to Figs. 3 and 4, which illustrate different geometric relations of diffusers in air-breathing engines. Referring to Fig. 3, sections of a spikey 10 Y ant commandV signal until the normal shock wave again and cowling 12 are shown onA one side of a common axis 32. In thisYcase, thegeometric arrangement is such thatV the minimum area, i. e., the diffuser throat, is behind Athe cowling lip, as indicated at 36. The arrangement is also such that for limited axialrmovement of the spike in either direction, the area at 36 will increase but will still be the smallest area within the'cowling. `It

is` well known that in this case, inlet aii is admitted to the kengine with maximum efficiency if the existing normal Vshock wave stands at the diiuser throat, because the diffuser throat is the point at which maximum pressure recovery` across the plane of the normal shock wave can be realized.

The location of the normal shock wave is also infiuenced by the conical shock waves, indicated at 38, and back pressure at therinner end of the diffuser. If the v spike were stationary, these effects would combine at the optimum speed to locate the normal shock wave at the diffuser throat. If flight conditions change, as by changes in engine scheduling which vary the back pressure, and

. changes in speed, the normal shock will move away from the dilfuser throat and less efficient admission of air to the engine will result. At speeds well below the optimum speed Ythe diffuser throat will be choked sufficiently to cause a normal shock wave to stand in front of the cowling inlet, as indicated at V40. As the optimum speed is approached the normal shock wave will stand between the cowling lip and the diffuser throat, and at speeds greater than the optimum the normal shock wave will move'inwardly past the throat. In accordance with this Y invention, the diffuser would be moved in the direction and through the distance necessary to maintainthe normal shock wave at the same location, i. e.,rthe diffuser throat. In this manner, inlet air is admitted to the env gine with maximum efficiency over a wide range of speeds.

Referring to Fig. 4, the throat of the diffuser formed by spike 10" and cowling 12 is at the lip of the cowling stands at the diffuser throat. If the change in flight conditions reflects a lower'Machrnumber, the new position of the spike will effect admission of inlet air to the engine at maximum efficiency for the lower Mach number, such as is indicated on curve 50 of Fig. 5.

The diffuser spike'may be adapted for movement in any suitable manner. For example, and as indicated in Fig. 2,'the spike may be threadedlyV supported on the end Yof a support rod or member 60 which extends through the center of the cowling 12. Iii such an `arrangement the spike is rotated to effectV axial movement thereof. Obviously, spike 10 could also be arranged in slidable engagementY with rod 60 and moved undercontrol of the actuator.

It will be apparent fromY methodY and Vmeans has been developed whereby an airbreathing engine for aircraft is enabled to operateat maximum efficiency by the provision of a movable center body which is positioned within the cowling of the engine in response to control signals resulting from a comparison'of the actual flight Mach number and the Mach number of air flow within the cowling.

What is claimed is: l

, l. In aircraft for flight at supersonic speeds,'in `comfbination with an air-breathing engine to rreceive air Vthrough the mouth of a cowling, a movable center body to form with said cowling a'diffuser for air entering the mouth of the cowling, the geometric arrangement of said center body and said cowling permitting a minimum diffuser throat` area to be maintained at a predetermined point from the mouth of the cowlingduring limited movement of said center body,fafirst Mach number transducer to develop an `output signal` representingY theV actual flight Mach number for the aircraft, position sensing means to establish a signal representing theinstant' position of said center body within said cowling, means responsive to the signals from saidfirst transducer and said position sensing means to develop Va function'sign'al which represents a desired Mach .numbery forvair flow within .the interior of the cowling behind the diffuser throat at said actual flight Mach number, a 'second Mach number transducer to develop a signal representative of the instant Mach number of the air flow within the interior of the cowling behind the diffuser throat, means responsive to the output signals from said second trans-Y 123', as indicated at 36 that is, the inlet area and the Y diffuser throat area coincide, and the geometry is such that this condition will be maintained for limited axial movement of the spike. For an arrangement of Vthis type, automatic control in accordance with this inven-Y tion causes the spike to be positioned to maintain the normal shock wave at the cowling lip for a wide range of speeds. v

Fig. 5 illustrates typically Vthe efficiency variation for different positions of a diffuser spike.VV Curves 50, 52 and 54 illustrate plots of for; successively greater VMach numbers, where my -enf gine efficiency, P=back Vpressure and A=diifuser throat l area. It will be observed that for each Mach number i there exists a point of Ymaximum efficiency, and the curve #falls 'off rapidlyv on either side ofY this criticalnpoint. lf.

Y cowling ,behindY the diffuser throat.

ducer and said function signal developing means to de- `velop a control signal, and actuating means to move said center body in accordance with the polarity and magnitude of said control signal to the position at which saidV flow within the desired Machl number exists for air 2.V Inrcombin'atio'n, in an air-breathing engine for supersonic aircraft,.a cowlingforfsaid engine having an entrance to receive inlet air, a lengtheof movable spike cen v tered at the entrance of said cowling, said spike andV said cowling providing a supersonic diffuser for'the inletvair,

z said spike having a geometry Vwhich effects'maintenance of a minimum diffuser throat area at a predetermined point from said entrance for limited axial movement Yof said spike, respective means to develop signals represent- Ving the'instant position of said spike and the Mach num- Y f bers of. air flow at opposite ends'of said spike, means responsive to said signals to develop a Ycontrol signal representative of the optimum position'of said spike at which maximum operatingfeiciency of the engine Twill Y be effectedat the instantspeed of the aircraft, and means Y the foregoing that a newV aat/e601.

for moving said spike to said optimum position in response to said control signal.

3. In combination with an air-breathing engine for aircraft own at supersonic speeds, wherein air is admitted to the engine through the mouth of a Cowling, a movable element centered at the mouth of the Cowling, said element and said Cowling forming a diffuser, said element being geometrically arranged within said Cowling to permit a minimum diiuser throat area within the Cowling to be maintained at a predetermined point for limited movement of said element, said element having rst and second positions at first and second Mach numbers to provide respective minimum throat areas at said predetermined point at which the Mach number of air ow behind said element is of a magnitude to effect admission of air to the engine at maximum eiiiciency, said element being located in said first position during flight at said first Mach number, lirst means operable upon Change in Hight speed to said second Mach number to develop an output signal representing said second Mach number, position sensing means for developing a signal which represents said first position of said element, second meansto develop a signal which bears a predetermined functional relation to the signals from said first means and said position sensing means, third means to develop a signal representative of the Mach number of the air ow at the interior of the Cowling behind the diiuser throat, means to compare the output signals from said second and third means and to develop a control signal which represents their difference, and means to move said element to said second position in response to said control signal.

4. In a supersonic aircraft having an air-breathing engine to which air is admitted through a Cowling, a center body centrally located at the entrance of the Cowling and extending partially to the exterior of the Cowling, said center body being symmetric with respect to and adapted for limited movement along the axis of the Cowling, said center body being dimensioned to maintain throughout said limited movement a minimum area at a predetermined point measured from the entrance of the Cowling, means to develop a signal representing the actual flight Mach number, means to develop a signal representing the Mach number of air flow within the Cowling and behind said predetermined point, means to Compare the position of said center body and the signals and to develop a command signal which represents the position of said center body to provide the minimum area through which air will be admitted to the engine with maximum eiliciency, an actuator mechanically coupledy to said center body and responsive to said command signal to move said center body along said axis to effect admission of air at maximum eliiciency.

References Cited in the file of this patent UNITED STATES PATENTS 

